Detecting Ovulation With a Basal Body Temperature Chart

BBT charts may also be able to detect early pregnancy

You can use a basal body temperature (BBT) chart to conceive faster by determining your most fertile days. Detecting ovulation with BBT charting is relatively easy, noninvasive, and inexpensive. Your gynecologist or reproductive endocrinologist may recommend charting to help detect when ovulation is happening or to get a better idea of your menstrual cycle patterns.

There are many advantages of BBT charting. Here’s everything you could want to know about basal body temperature charting.

What Is BBT?

Your BBT is your temperature when you’re at complete rest. It changes based on a number of factors, including your hormones.

When you ovulate, the hormone progesterone causes your temperature to rise. It remains higher throughout the rest of the menstrual cycle. Then, just before your period starts, the hormone progesterone drops. This means your basal body temperature will drop too—unless you’re pregnant, in which case your temperatures will remain higher because progesterone will stay high.

To check your BBT is, you must take your temperature in the morning before you get out of bed or move around. You can’t go to the bathroom quickly first. That will cause your temps to rise just slightly, enough to make your chart inaccurate.

It's also essential that you take your temperature correctly. Otherwise, your temperature will not be accurate, and you may not be able to detect ovulation. 

Advantages of BBT Charting

BBT charting can:

Choosing a BBT Chart

The first step to charting your basal body temperature is getting a chart to record your temperature. You can find sample charts in some fertility books, such as Take Charge of Your Fertility (Harper Perennial)—a book considered by many to be the go-to resource for basal body temperature charting guidance.

Another option for charting is fertility awareness software, also known as fertility calendars. There are several fertility calendar options online, and several fertility apps for your phone. Many of them are free.

You can also make your own graph. If you make your own, you will want to plot the temperature along the vertical, allowing one-tenth of a degree for each square. Along the horizontal, you will have the days of your cycle.

Most people prefer using a digital tool because you can log a ton of information and reduce the chance of human error. Most ovulation software will automatically indicate when ovulation likely occurred. If you try plotting the temperature yourself, you might worry about making a mistake.

How to Measure BBT

Once you have something to record your temperature on, it's time to start taking your basal body temperature. You will need a thermometer. There are thermometers made especially for tracking your body basal temperature.

While some come with interesting features, the truth is that any good thermometer will work. Ideally, you should use one that is accurate to 1/10th (98.6) of a degree if you measure in Fahrenheit or 1/100th (37.00) of a degree in Celsius.

Use the same thermometer throughout the cycle. If you buy a new one, start using it on day one of the next cycle.

Taking your BBT is not too hard. There are a few important guidelines, though.


Take your temperature at the same time (plus or minus no more than 30 minutes) every morning. For example, if you take it at 7:30 a.m. every weekday, don't take it earlier than 7 a.m. or later than 8 a.m. on other days.


Avoid getting up, sitting up, walking around, or going to the bathroom before taking your temperature. The minute after you wake up, you need to pop the thermometer in your mouth.


Make sure you have had at least three to four straight hours of sleep before taking your temperature in the morning. If you stayed up all night, or you woke up and walked around at night repeatedly, it will throw off your results.

When to Start Charting

Ideally, you should start charting on the first day of your period and continue to take your BBT every morning throughout the entire cycle. Every day, mark your waking basal body temperature, along with the time that you took your temperature.

After you have experience with charting, you may discover that you can skip the first few days of your period and start taking your temperature around day five or seven. Until you know when you tend to ovulate, though, it is best to take your temperature all the way through the cycle.

Identifying Ovulation

With BBT charting, you are looking for an overall pattern, as opposed to a temperature spike here or there. Your temperature may rise and fall as your cycle progresses, but you should notice a biphasic pattern after ovulation. This means that before ovulation, the temperatures are on average lower than they are after ovulation.

After you see at least three higher-than-average temperatures in a row, you can most likely say that ovulation occurred on the day before the first high temperature. If you have also been tracking your cervical mucus, then you can be even more sure ovulation occurred on the day before if you noticed fertile cervical mucus on the days leading up to the temperature rise.

If you are lucky, you may notice a sharp dip in temperature on the day of ovulation. Not every person gets this handy heads-up. If you do notice a consistent dip in temperature before the rise from month to month, you should be sure to have sexual intercourse on that day.

Getting Pregnant

The primary way to use a BBT chart to get pregnant is to look for patterns. Do you tend to ovulate on certain days of your cycle? Use this information to time intercourse better.

For example, if over a three-month period you note that ovulation occurred on days 11, 12, and 15, then on your next cycle, you probably want to time sex between days 6 through 16, with special attention toward days 11 through 15.

Timing Sex

You don't need to have sex on the day of ovulation to get pregnant. If you have sex just a few times during the days before ovulation, that should be enough to get the sperm to the egg in time. Some couples try to have sex every other day the week before they expect ovulation. This is also a good plan.

Other Data to Track

To make charting most effective for you, you can track more than just your morning temperature. Here is some other info you may want to notice and indicate on your chart.

Days You Have Sex

This will help you and your healthcare provider see if you are timing intercourse right. There are only five to seven days within each cycle when it's possible for sex to lead to pregnancy. The two to three days right before ovulation are best. You don't want to miss your window of opportunity.

Another reason for charting when you have sex is to show how often you are having sexual intercourse. If male factor infertility is an issue, having sex every day may decrease your chances for pregnancy. On the other hand, having sex just once within the approaching days to ovulation may not be enough.

Cervical Mucus

If you track only one other thing besides your BBT, cervical mucus should be it. That's because your basal body temperature can only tell you that you ovulated after it happens.

By the time you see three higher-than-average temperatures, your most fertile days have passed. However, your cervical mucus can tell you when you are about to ovulate. You can use that information to know when to have sex.

Cervical Position

Besides tracking your cervical mucus, you can also track your cervical position to help predict ovulation. Your cervix will become higher, softer, and more open as ovulation approaches. After ovulation, the cervix becomes firmer, lower, and closed (or partially closed).

Lifestyle Considerations

It's also helpful to track illnesses, your sleep schedule, and your stress levels. Even a relatively benign cold can mess with your BBT charting. If sinus congestion forces you to sleep with your mouth open, for example, your temperature may be thrown off. Also, poor sleeping habits can skew the results and even stress can have an impact on your BBT.

Ovulation Kit Results

If you're also using an ovulation predictor kit or any other ovulation prediction technology, you should mark down these results on your chart as well. This information can be useful in identifying patterns that are unique to your body.

What If You’re Not Ovulating?

signs you may not be ovulating
Verywell / Kelly Miller

One of the advantages of charting is that it allows you to see whether you are ovulating. If you are not ovulating, you cannot get pregnant. If you are ovulating irregularly, it may indicate a possible infertility risk

Lack of ovulation is called anovulation and is a common cause of female infertility. Most people with anovulation can take fertility drugs to trigger ovulation and hopefully help them get pregnant. Clomid is the most well-known fertility drug used to treat anovulation.

Signs on your chart that may indicate that you’re not ovulating include:

Pregnancy and Your BBT Chart

Can your BBT chart tell you whether you are pregnant or not? Yes and no. During the two-week wait, many people notice temperature fluctuations and wonder if they are early pregnancy signs. There are four ways a BBT chart can indicate a pregnancy or the possibility of pregnancy.

Sex on Most Fertile Days

A BBT chart can help you determine if you have had sex on your most fertile days. Although your basal body temperature can’t predict ovulation, you can determine if and when you ovulated a few days after it happened in a BBT chart.

This means you may not know if you had sex on the “right days” until after ovulation occurs. But you can look back on your chart and determine this. You are most likely to conceive if you had sex on the two days preceding ovulation.

Implantation Dip

An implantation dip is a one-day drop in temperature about a week after ovulation. The majority of the time, an implantation dip is nothing more than a mid-cycle dip in temperature and does not indicate pregnancy. It’s debatable whether or not this is a possible sign of early pregnancy.

Triphasic Pattern

A triphasic temperature pattern is a second temperature increase occurring about one week after ovulation. Seeing a triphasic pattern on your BBT chart is slightly more likely to indicate a potential pregnancy, but it is also no guarantee.

A triphasic pattern indicates that progesterone rose a little bit more, causing your temperatures to also rise slightly more. This may occur because you’re pregnant. That said, it also could happen when you’re not.

Long Luteal Phase

The most reliable way to detect pregnancy on a BBT chart takes patience. The old-fashioned method of doing this involves waiting to see if your luteal phase—the time between ovulation and your expected period—is longer than usual.

For most people, the luteal phase does not vary by more than a day or two from month to month, even if the length of their menstrual cycle does vary. For example, a cycle length may range from 30 and 35 days, but the luteal phase is consistently 12 or 13 days long.

If you see that your luteal phase has gone at least one day past the usual length, you might be pregnant. If it goes two days past the longest luteal phase you’ve ever had, the likelihood of being pregnant is even higher. This is a good time to take a pregnancy test.

If you reach 18 days past ovulation and you still don’t have your period, chances are very good that you are pregnant. Not many people can wait that long without taking a pregnancy test. Still, it is the strongest early sign of pregnancy detectable with a BBT chart.

A Word From Verywell

Basal body temperature charting is a great way to track your cycles and ovulation patterns. It can also help your healthcare provider detect possible ovulatory infertility. If you are concerned that you are not ovulating, bring your BBT chart to your gynecologist.

When it comes to detecting pregnancy, BBT charts can only offer small hints. You can't confirm pregnancy with a fertility calendar. The best way to use your time and energy during the two-week-wait is to focus on self-care and to distract yourself with your life beyond trying to conceive. 

Frequently Asked Questions

  • Can your BBT drop and you still be pregnant?

    While you are more likely to see a one-day temperature drop in your BBT if you are pregnant, it is not a definitive sign that you are in fact pregnant. You could see a small dip on your chart almost every month and still not be pregnant.

  • Does BBT rise after implantation?

    With an implantation dip, the fall in your temperature only lasts a day—your temperature goes back up the next day. This is unlike what happens after your period begins when your temperature will drop and stay down. Still, you cannot rely on a suspected implantation dip to indicate pregnancy. You will still need a pregnancy test to confirm.

  • How many days after implantation can you test positive?

    It is hard to predict the exact timing of implantation, which means the closer you test to your next period, the more accurate your pregnancy test will be. Even though some tests advertise being able to predict pregnancy up to six days before you miss your period, you will get a more reliable result if you wait until you have missed your period to take a pregnancy test.

4 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Sharpe RM. Sperm counts and fertility in men: a rocky road ahead. Science & Society Series on Sex and Science. EMBO Rep. 2012;13(5):398-403. doi:10.1038/embor.2012.50

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By Rachel Gurevich, RN
Rachel Gurevich is a fertility advocate, author, and recipient of The Hope Award for Achievement, from Resolve: The National Infertility Association. She is a professional member of the Association of Health Care Journalists and has been writing about women’s health since 2001. Rachel uses her own experiences with infertility to write compassionate, practical, and supportive articles.